Polymer Technology - What Is Polymerization & Degree Of Polymerization?

What Is Polymerization?

The chemical process in which lower molecular weight substances [monomers] are bond together to form high molecular weight substances [polymers] is known as polymerization.

 

Why Polymerization?

Polymers [products of the polymerization process] offer lots of extensive properties as compared to the other natural or synthetic products. These extensive properties of polymers include:

• Higher strength


• Resistance to corrosion


• Easy to fabricate - Can be molded in any shape, size and color


• Improved performance


• Reduced product costs


• Reduced weight [because of improved ratio of strength to stiffness]


• Most of them are good electrical insulators [such as plastics]; However some are good electrical conductors too [carbon black mixed polymers].

 

Degree Of Polymerization:

Degree of polymerization refers to the number of monomers in polymer molecules. This degree of polymerization is directly related to the polymer properties, such as melting point, mechanical strength, etc.

For homopolymers , degree of polymerization can be calculated as:

 

 [latex size=0 color=000000 background=ffffff]\displaystyle X_{n} = \frac{M_{n}}{M_{o}} [/latex]

Where,

           [latex size=0 color=000000 background=ffffff]\displaystyle X_{n} [/latex]     =  Degree of polymerization

                    [latex size=0 color=000000 background=ffffff]\displaystyle M_{n} [/latex]      =  Total molecular wt. of Polymer

  [latex size=0 color=000000 background=ffffff]\displaystyle M_{o} [/latex]        =  Molecular wt. of Polymer unit

 

Mechanisms Of Polymerization:

Polymerization processes or mechanisms of polymerization can be divided into two groups:

• Condensation polymerization [or step growth polymerization]


• Addition polymerization [or Chain growth Polymerization]

 

Types Of Polymerization

Polymerization process requires quantity of monomers along with the initiator or catalyst to start the reaction.  Polymerization processes can be classified in terms of the reaction mediums; i.e.

• Bulk polymerization


• Solution polymerization


• Suspension polymerization


• Slurry polymerization

Read More

Classification Of Materials-What Are Different Types Of Materials?

[caption id="attachment_268" align="alignright" width="320" caption="Different types of materials"][/caption]

There are hundreds and thousands of different types of materials, present in this world. Some are naturally occurred materials [such as wood, water, clay, etc.] and some are men made materials-extracted from the naturally occurred materials by manipulating properties of them. It is impossible to study each and every material separately under the tree of material science, so these materials are divided into several categories, on the basis of the following factors:

• Chemical composition of materials,


• Mode of occurrence of materials naturally


• Ways of extraction of materials before usage [refining, manufacturing, etc.]


• Structure of materials [atomic or crystalline]


• Use of material [industrial and technical]

Most general classification of materials leads following different types of materials groups

Metals

This category contains all metals, whether they are ferrous, non-ferrous or alloys. Metallic materials are usually combination of several metallic elements. They have large number of free electrons; and these free electrons make metals good conductor of electricity and heat. Metals are generally defined as:

“All those substances which can readily give-up electrons to form metallic bonds are considered as metals”.

Some of the specific properties of metals are plasticity, strength, hardness, high luster, good conductor of heat and electricity, stiffness, malleability, magnetic properties, etc. These metallic materials are further classified into three different categories according to their end usage.

• Pure Metals: Extraction of pure metal is not an easy task, these are usually obtained by refining the ores by very expensive specialized extraction techniques. Some of the important pure metals are copper, aluminum etc.

• Ferrous Metals : Iron or ferrous is the main constituent of these ferrous metals. Ferrous metals are extremely important for engineering processes.

• Alloys : when two or metals are blended together [or at least one being metal], they form alloys. Most common example of alloy is stainless steel, which is the formed by the blend of chromium, nickel and low carbon steel.

Polymers:

Polymer materials consist of rubber and plastic constituents and possess very large molecular structures. Many of polymeric compounds falls in the organic materials categories, which are composed of carbon and hydrogen along with other non-organic materials. Polymers are extremely flexible in nature and possess low densities.

Ceramics:

Ceramics are intermediate compounds fall between the categories of metallic and non-metallic materials. Most frequently, these are oxides, carbides and nitrides. Ceramic materials are resistant to harsh environments such as high temperatures, due to which these are used as heat and electric insulators.

Composites:

Composites are the materials, which consist of more than one type of material to display a combination of best properties or characteristics of respective materials. A very familiar example is fiber glass, in which a polymeric material is embedded with glass fibers. Fiberglass acquires flexibility from the polymer and strength from the glass material.

Semi-Conductors:

As it is clear from their name, semi-conductors are intermediate between electrical insulators and conductors. Their electrical characteristics are extremely sensitive towards the presence of impurities, even in small percentages. Semi-conductors have totally revolutionized the electronics and telecom industry with the invention of integrated circuits.

Bio Materials:

Bio-materials are generally used in components related to human body implants in order to replace the diseased or malfunctioning organs. The basic criteria while selecting material for bio-materials are they must be compatible with human body [i-e: human body must accept them as their part], These materials must not produce toxins while in the human body. The materials which can be used as bio-materials now these days are ceramics, polymers, metals and semiconductors

Advanced Materials:

Advanced materials are utilized in high-tech [or high technology] applications. High technological processes refers to those processes which functions on relatively sophisticated and intricate principles such as fiber optics, computer systems, electronic equipment [LCDs, CD players, VCRs, etc.], military operations, space ships, air crafts, etc. These materials are very expensive and may be off all types [ceramics, polymers, metals, etc.].

Read More

What is material science?

[caption id="attachment_262" align="alignright" width="320" caption="Structure Of Material"][/caption]

Material science and engineering plays most important and vital role in this modern age of technology. It is basically the integration of natural sciences [physics, chemistry and biology] along with technical approaches. It helps in facing challenges by integrating education and research with versatility, breadth and perspective. So, Materials engineering covers detailed study of all materials, by investigating the relationship between basic structures and the properties of materials.

More elaborately, materials engineering revolves around the study of following factors:

• Structures of Materials

The basic structure of materials refers to the arrangement of internal components of materials. The structures are divided into four categories – subatomic, atomic, microscopic and macroscopic.

• Properties Of Materials

 Properties of materials describe the response of materials on exposition to some external factors, such as mechanical, electrical, etc.  Material properties depend upon the composition of materials as well as upon the microscopic structure of the material. Properties of materials have already been discussed here: Properties of materials

• Molecular Or Atomic Motion

 I.e. Study of interaction or motion between the atoms or molecules within the material.

• Manufacturing Processes:

 Generally, the materials are considered as of two types, naturally occurred materials and the men made materials. Manufacturing processes refers to the processes which are used to manufacture the materials by manipulating the properties of materials. These processes vary from one material type to another, as well depends upon the operating conditions of the process.

• Mechanisms Of Degradation Of Materials:

Degradation of materials is the most important factor covered under materials engineering education. Degradation simply means the failure of a material. In order to prevent the failure of materials, it is necessary to study about the mechanisms of degradation of materials. Some of the common materials degradation factors are corrosion, abrasion, tribology, etc.

Materials sciences and engineering is a broad discipline of engineering and works with the collaboration of other disciplines of engineering [such as electrical, mechanical, chemical, biomedical, etc.] for better performance and reliability of the product. So, the basic goal of a materials engineer is not only study, design and modify the materials for the process design, but also to apply their experience and knowledge towards product design and optimization.

Read More

Paper Recycling Process-How To Recycle Paper?

[caption id="attachment_240" align="alignright" width="320" caption="how to make recycled paper"][/caption]

Paper is one of the most important recyclable materials. What is paper recycling, and what is the importance of paper recycling has already been discussed here…” recycled paper”.

The whole paper recycling process can be divided into two basic stages. First one is pre-processing stage [involves collection, sorting and the transportation of the waste paper], while the other one is the processing stage [processing of junk paper to the final products].

Pre-processing stage

The pre-processing stage of paper recycling involves following steps:

• Collection & Transportation:

The paper is first collected and transported to the respective locations.

• Sorting:

The collected paper is then sorted out on the basis of types or grades of paper.

• Storage:

The paper is then stored in the warehouses for further processing.

Processing Stage:

The processing stages are the main stages involved in the recycling of used paper to the manufacturing of newer products. This processing stage involves:

• Pulping:

The stored paper is then moved by the conveyor belt to the “Pulper” – A big unit contains dissolving chemicals and water. Firstly, the paper is chopped into small pieces, then into tiny strands of cellulose because of heating. This mixture of water, chemicals and tiny strands of cellulose is termed as “Pulp”.

• Screening

The pulp from the pulper is then passed through screens of different sizes. The purpose of screening is to remove small contaminants [like glue, plastic, sand, etc] from the pulp.

• Cleaning

The screened pulp is then introduced into large cylinders [cone-shaped], which are set to rotation or spinning [same as sedimentation process], due to which the heavy contaminants such as staples are settled at the bottom of the cylinder, while the lighter contaminants are collected in the center of the cone.

• De-inking:

After cleaning, the pulp undergoes through a pulp laundering process, known as de-inking. Deinking will remove the printing ink and other sticking materials like glue, adhesives, etc. Usually a combination of two deinking processes is used. Washing helps in rinsing the smaller ink particle from pulp with the help of water, while the stickies and larger particles are removed with air bubbles in floating process.

• Refining:

During refining process, pulp is beaten to ensure the separation of large bundles of fibers into individual fibers.

• Bleaching & Color Striping:

The selection of bleaching and color striping process depends upon the type of paper to be made.

If the colored paper is to be produced, the, the color stripping process is used. The stripping chemicals help in removing the dyes from the paper.

Bleaching is used in case of white paper production. Paper is bleached with oxygen, chlorine dioxide or hydrogen peroxide.

For brown paper production, pulp is neither stripped, nor bleached.

• Paper Making

Finally, the clean pulp is ready to be processed as paper in the paper machine. Paper machine itself consists seven different sections, which are flow box, wire, presser, drier, size press, calendaring section and reeling up section.

The pulp can be used alone, or can be blended with newer material [virgin fiber] to add strength and smoothness to the paper. Rest of the recycled paper making process is same as that of the simple paper making process, which can be read here…”Paper Manufacturing”.

Read More

Recycling Paper – What is Paper Recycling & Importance Of Recycled Paper

[caption id="attachment_224" align="alignright" width="181" caption="recycle paper"][/caption]

Recycling is the process of producing new products or materials by reprocessing used materials. There are number of materials, which can be recycled to some other useful materials. Some of them are paper, plastic, cardboard, glass, metal [such as steel, aluminum etc]. More about Recycling can be studied here… “What is recycling”.

Paper is made from cellulose – A plant fiber which is derived from wood. This cellulose is converted to pulp first then this pulp is used for the manufacturing of paper. More about paper and paper manufacturing has been discussed in detail here… “Paper manufacturing”.

About one-third of the total solid waste generated around the globe is paper waste. If the world is able to recycle only 50% of the paper then millions of trees can be saved globally. Recycling paper not only saves the energy consumption, but it also helps in reducing the air pollution [caused by the burning of paper]. The complete paper recycling procedure is discussed here…”how to recycle paper”.

What Is Paper Recycling:

Paper is recycled by converting waste paper [thrown by the consumers after use] and scrap paper [wastage in industrial pre-production level] into new usable products. Certain categories of paper, which can be recycled, are:

• Mill broke – Scrape from the paper manufacturing processes such as trimmed papers, paper pulp, etc


• Pre-Consumer Waste - Material discarded before consumer usage.


• Post-Consumer Waste – Discarded material after consumer usage, such as newspaper, office paper, notebooks, etc

What Can Be Made From The Paper Recycling:

Usually the recycled paper made from the paper recycling is of low grade then that of the original material. E.g. the fine office paper sheets can be recycled to make the newspaper, etc.  Almost 80% of the recovered paper is recycled back to form the paper or other paper related products. Rest of the 20% recycled paper can be used for the production of other products, such as wall insulations, ceilings, fuel, roofing, paint filter, animal bedding, etc.

Read More

Recyclable materials – What Can Be Recycled

[caption id="attachment_83" align="alignright" width="300" caption="recyclable materials"][/caption]

Recycling and the benefits of recycling have already been discussed in the previous post. Have a look here: What is recycling.

Materials Which Can Be Recycled:

All materials are not considered as good recyclable materials. The biodegradable materials like food items, organic wastes, etc are not considered as the recyclable materials. The materials, which can be picked, cleaned, and reprocessed into new materials are considered as the recyclable materials. The good recyclable materials are:

Municipal Solid Wastes

These municipal solid wastes (MSW) are the post-consumer solid wastes, generated by the domestic units, commercial units, institutions, hospitals, etc. MSWs are not easy to define; however, MSW is considered as the material waste generally (yard waste, papers, glass, metals, etc). Some of the MSW are described under:

o   Paper

Wasted papers are recycled into the new paper products by paper recycling. It is unfortunately a fact that the paper processing requires pulp, which is obtained by cutting down the trees, which is a threat to the environment. Using recycled papers can minimize the new paper requirements, and so are the wood requirements.

o   Glass

Unlike paper recycling, glass recycling needs extra concentration. The glass bottles and the other types of glass (like Pyrex, light bulbs, window glass, auto glass, etc) cannot be recycled together. As glass chemistry is based on its oxide components typically. The most likely recyclable glass is the clean glass.

o   Oil

Oil recycling might be newer for many people. “Oil” refers to variety of combustible liquids, which are not soluble in water and leave greasy stain. The used or contaminated oil (not consumed) can be considered as the recyclable material. Direct combustion of used oil as a burner fuel should always be condemned, because it not only destroys this valuable source, but also cause environmental pollution.

o   Plastic

Plastic recycling has turned a new shape today. There are lots of grades of plastics. And all the grades or types of plastics cannot be recycled together. A very small quantity of the wrong grade of the plastic can ruin the whole processing batch. It is generally not easy to separate different grades of the plastics. That’s why, there are several cryptic markers used in the plastic industries to indicate the type of the plastics.

o   ferrous metals

Recycling of the ferrous scrap is the principle recycling activity worldwide. The ferrous metals refer to the substances made up of iron or steel. Recycling of these ferrous metals gives number of environmental benefits as well including reduction in air pollution, water usage, landfill requirements, etc compared to the use of virgin materials.

o   Non ferrous metals

Non ferrous metals are any metal other than iron or iron alloys. Highly recycled non ferrous metals are copper, aluminum, lead and zinc.

o   Rubber

Rubber recycling is commonly known by the name of “tire recycling”. Used and damaged tires, which cannot longer be used on the roads, are one of the largest sources of the hazardous wastes. That’s why the tires are one the most recyclable materials. Rubber is a very resilient material, and can easily be reused in other products.

Waste Water Recycling

Waste water recycling refers to the process of removing suspended solids, impurities, Ph balancing, color treatments etc. There are various ways, in which waste water can be recycled. The selection of the treatment process depends upon the end use of the treated water. If the water is to be treated for the textile industrial usage, then there might be some of the treatment techniques involved like the sedimentation, filtration, color treatments etc. But, if water is being treated for human consumption, then number of additional processes like ultra-filtration, reverse osmosis, etc should be carried out. However, treated waste water is generally not used for the drinking purposes.

Read More

Recyclable materials – What Can Be Recycled

Recycling and the benefits of recycling have already been discussed in the previous post. Have a look here: What is recycling. 

Recyclable Materials

What Materials Can Be Recycled:

All materials are not considered as good recyclable materials. The biodegradable materials like food items, organic wastes, etc are not considered as the recyclable materials. The materials, which can be picked, cleaned, and reprocessed into new materials, are considered as the recyclable materials. The good recyclable materials are:

   

   

Municipal Solid Wastes 

These municipal solid wastes (MSW) are the post-consumer solid wastes, generated by the domestic units, commercial units, institutions, hospitals, etc. MSWs are not easy to define; however, MSW is considered as the material waste generally (yard waste, papers, glass, metals, etc). Some of the MSW are described under:

o   Paper

Wasted papers are recycled into the new paper products by paper recycling. It is unfortunately a fact that the paper processing requires pulp, which is obtained by cutting down the trees, which is a threat to the environment. Using recycled papers can minimize the new paper requirements, and so are the wood requirements.

o   Glass

Unlike paper recycling, glass recycling needs extra concentration. The glass bottles and the other types of glass (like Pyrex, light bulbs, window glass, auto glass, etc) cannot be recycled together. As glass chemistry is based on its oxide components typically. The most likely recyclable glass is the clean glass.

o   Oil

Oil recycling might be newer for many people. “Oil” refers to variety of combustible liquids, which are not soluble in water and leave greasy stain. The used or contaminated oil (not consumed) can be considered as the recyclable material. Direct combustion of used oil as a burner fuel should always be condemned, because it not only destroys this valuable source, but also cause environmental pollution.

o   Plastic

Plastic recycling has turned a new shape today. There are lots of grades of plastics. And all the grades or types of plastics cannot be recycled together. A very small quantity of the wrong grade of the plastic can ruin the whole processing batch. It is generally not easy to separate different grades of the plastics. That’s why, there are several cryptic markers used in the plastic industries to indicate the type of the plastics.

o   ferrous metals

Recycling of the ferrous scrap is the principle recycling activity worldwide. The ferrous metals refer to the substances made up of iron or steel. Recycling of these ferrous metals gives number of environmental benefits as well including reduction in air pollution, water usage, landfill requirements, etc compared to the use of virgin materials.

o   Non ferrous metals

Non ferrous metals are any metal other than iron or iron alloys. Highly recycled non ferrous metals are copper, aluminum, lead and zinc.

o   Rubber

Rubber recycling is commonly known by the name of “tire recycling”. Used and damaged tires, which cannot longer be used on the roads, are one of the largest sources of the hazardous wastes. That’s why the tires are one the most recyclable materials. Rubber is a very resilient material, and can easily be reused in other products.

·    Waste Water Recycling

Waste water recycling refers to the process of removing suspended solids, impurities, Ph balancing, color treatments etc. There are various ways, in which waste water can be recycled. The selection of the treatment process depends upon the end use of the treated water. If the water is to be treated for the textile industrial usage, then there might be some of the treatment techniques involved like the sedimentation, filtration, color treatments etc. But, if water is being treated for human consumption, then number of additional processes like ultra-filtration, reverse osmosis, etc should be carried out. However, treated waste water is generally not used for the drinking purposes. 

Read More

What Is Recycling And What Are The Benefits Of Recycling?

[caption id="attachment_88" align="alignright" width="240" caption="what is recycling"][/caption]

The process of manufacturing or producing new, useful and marketable materials from the waste or the junk substances is known as recycling. It is an old aged process, and people have been recycling their household or business goods for thousands of years, to save materials and so is the cost. However, importance and benefits of recycling got noticed in the mid 1980’s on the industrial level. Recycling is not only beneficial for the household level, but also important for the nation’s economic dependence. Also, recycling shares a major part to save the environment.

Although, the trend of recycling is growing, but still there is need to educate a common person about the recycling, and that how a common person can become the active part of the society because of recycling. Recycling doesn’t require huge industrial setups, and can be done on a very small scale; making use of an empty coke tin is also recycling. However, it is important to know that what materials can be recycled. On large scale, Steel and paper industries are the biggest cost saving sectors because of recycling. The basic purpose of this post is to introduce recycling and discuss about the benefits of recycling.

Benefits Of Recycling:

There are numerous benefits of recycling, which can take long time to discuss. However, some of the key benefits of recycling are:

• The basic purpose of recycling is truly the main benefit too. Recycling turns waste materials into useful and valuable resources.


• It conserves the natural resources, like minerals, water, trees, etc.


• It reduces the need of incineration and land filling.


• It is helpful in preventing pollution, caused by in case of using virgin materials.


• Recycling decreases greenhouse emissions, and so is the global climate change.


•  Recycling saves energy.

Some Interesting Recycling Facts:

• A common person makes an average of 2 kg (around 4.7 pounds) daily.


• Every ton of aluminum cans recycling can conserve more than 1500 gallons of gasoline.


• Glass can be recycled again and again for many times. One glass bottle recycling can save up to 400-watt electricity (you can light a 100 watt bulb for 4 hours).


• For the production of 1 ton newspaper, approx 24 trees are needed. In case of recycling, these saved trees can absorb around 250 pounds of carbon dioxide, present in the air, annually.


• The cost of plastic recycling (especially the PET bottles) is almost half of the cost of plastic incineration.

Read More

What Is Recycling And What Are The Benefits Of Recycling?

What is Recycling

The process of manufacturing or producing new, useful and marketable materials from the waste or the junk substances is known as recycling. It is an old aged process, and people have been recycling their household or business goods for thousands of years, to save materials and so is the cost. However, importance and benefits of recycling got noticed in the mid 1980’s on the industrial level. Recycling is not only beneficial for the household level, but also important for the nation’s economic dependence. Also, recycling shares a major part to save the environment.

Although, the trend of recycling is growing, but still there is need to educate a common person about the recycling, and that how a common person can become the active part of the society because of recycling. Recycling doesn’t require huge industrial setups, and can be done on a very small scale; making use of an empty coke tin is also recycling. However, it is important to know about the recyclable materials. On large scale, Steel and paper industries are the biggest cost saving sectors because of recycling. The basic purpose of this post is to introduce recycling and discuss about the benefits of recycling.

Benefits Of Recycling:

There are numerous benefits of recycling, which can take long time to discuss. However, some of the key benefits of recycling are:

• The basic purpose of recycling is truly the main benefit too. Recycling turns waste materials into useful and valuable resources.
• It conserves the natural resources, like minerals, water, trees, etc.
• It reduces the need of incineration and land filling. 
• It is helpful in preventing pollution, caused by in case of using virgin materials.
• Recycling decreases greenhouse emissions, and so is the global climate change.
• Recycling saves energy.

Some Interesting Recycling Facts:

We have found some very interesting recycling facts; which are:

• A common person makes an average of 2 kg (around 4.7 pounds) daily. 
•  Every ton of aluminum cans recycling can conserve more than 1500 gallons of gasoline.
• Glass can be recycled again and again for many times. One glass bottle recycling can save up to 400-watt electricity (you can light a 100 watt bulb for 4 hours).
• For the production of 1 ton newspaper, approx 24 trees are needed. In case of recycling, these saved trees can absorb around 250 pounds of carbon dioxide, present in the air, annually.
• The cost of plastic recycling (especially the PET bottles) is almost half of the cost of plastic incineration.

Read More

What Is Radiation Heat Transfer

[caption id="attachment_208" align="alignright" width="270" caption="radiation heat transfer"][/caption]

Radiation heat transfer is basically the energy transfer via electromagnetic waves. Before going into details about radiation heat transfer, it is essential to understand the radiations first.

What Are Radiations?

Radiations are defined as the electromagnetic waves having wavelength of 0.1 to 100 microns, which doesn’t require any medium to travel. Radiation waves are classified into two types; ionizing radiations and non ionizing radiations. Ionizing radiations have the tendency (because of having sufficient energy) to ionize an atom. Non-ionizing radiations cannot ionize an atom (heat waves, radio waves and light waves are the examples of non-ionizing radiations).  Hence, in physics on nuclear engineering, we deal with the ionizing radiations, while here; non-ionizing radiations are of our main interest.

 Image: Salvatore Vuono

What Is Radiation Heat Transfer?

According to the quantum theory, radiations consist of energy packets (named as photons), that has no rest mass and move at the velocity of light. So, radiation heat transfer basically deals with the exchange or transfer of that energy between the bodies.  Every object, having temperature greater then absolute zero (0 K) emits radiations. Mostly, the solids are considered as the radiation emitters, because the energy emitted by the fluid particles is usually absorbed by the nearby molecules, and thus this energy cannot reach the surface. These emissions are directly proportional to the temperature of the body; the higher the temperature, higher will be the radiations emissions.

Hence:

Ever object, above absolute zero temperature emits energy carrying electromagnetic radiations. When these radiations fall on the other object, some energy is transferred from the radiation waves to the object. This transferred energy is known as the radiation heat transfer.

Emissivity:

Emissivity is the tendency of an object to release electromagnetic radiations per unit area and per unit time. In order to calculate the radiation emissive power, we assume an ideal surface, which can absorb and radiate all wavelength radiations. This ideal surface is named as the black body, or the ideal radiator. However, the heat flux of the real surface is less than that of the black body. According to Stefan Boltzmann’s law:

E = ԑσ T_s⁴

Where:

E             =             Emissive power of real surface;  (W/m²)

ԑ             =             Radiative property of the surface.

σ             =             Stefan Boltzmann constant;          (5.67 x 10^-8 W/m².K⁴)

T_s            =             Absolute temperature;                   (K)

Read More

What Is Radiation Heat Transfer

Radiation heat transfer is basically the energy transfer via electromagnetic waves. Before going into details about radiation heat transfer, it is essential to understand the radiations first.

What Are Radiations?

Radiations are defined as the electromagnetic waves having wavelength of 0.1 to 100 microns, which doesn’t require any medium to travel. Radiation waves are classified into two types; ionizing radiations and non ionizing radiations. Ionizing radiations have the tendency (because of having sufficient energy) to ionize an atom. Non-ionizing radiations cannot ionize an atom (heat waves, radio waves and light waves are the examples of non-ionizing radiations).  Hence, in physics on nuclear engineering, we deal with the ionizing radiations, while here; non-ionizing radiations are of our main interest.

What Is Radiation Heat Transfer?

According to the quantum theory, radiations consist of energy packets (named as photons), that has no rest mass and move at the velocity of light. So, radiation heat transfer basically deals with the exchange or transfer of that energy between the bodies.  Every object, having temperature greater then absolute zero (0 K) emits radiations. Mostly, the solids are considered as the radiation emitters, because the energy emitted by the fluid particles is usually absorbed by the nearby molecules, and thus this energy cannot reach the surface. These emissions are directly proportional to the temperature of the body; the higher the temperature, higher will be the radiations emissions. 

Hence:

Ever object, above absolute zero temperature emits energy carrying electromagnetic radiations. When these radiations fall on the other object, some energy is transferred from the radiation waves to the object. This transferred energy is known as the radiation heat transfer. 

Emissivity:

Emissivity is the tendency of an object to release electromagnetic radiations per unit area and per unit time. In order to calculate the radiation emissive power, we assume an ideal surface, which can absorb and radiate all wavelength radiations. This ideal surface is named as the black body, or the ideal radiator. However, the heat flux of the real surface is less than that of the black body. According to Stefan Boltzmann’s law:

E = ԑσ T_s⁴

Where:

E             =             Emissive power of real surface;  (W/m²)

ԑ             =             Radiative property of the surface.

                σ             =             Stefan Boltzmann constant;          (5.67 x 10^-8 W/m².K⁴)

T_s               =             Absolute temperature;                  (K)

Read More

What Is Convection?

 

[caption id="attachment_210" align="alignright" width="300" caption="convection heat transfer"][/caption]

What Is Convection:

Convection is the mechanism of heat transfer occurs as a result of movement of fluid on a macroscopic scale. I.e. heat transfer due to the mixing of elements in fluid or the heat transferred from a solid surface to the moving fluid.

There are several factors, on which heat transfer by convection depends on, such as fluid thermal conductivity, fluid density, fluid velocity, solid surface roughness, temperature difference between fluid and solid surface, moving fluid turbulence, etc. however, as a general rule, it has been experimentally proven that the higher the fluid velocity, the higher is the convective heat transfer coefficient [some times called as film conductance, because of its relation to the conduction process].

Difference Between Conduction And Convection:

It generally doesn’t make sense trying to differentiate between the conduction and convection; as it is the same energy, which is transferred by the combined action of conductivity and the movement of the fluid. Initially, the energy is delivered from solid to the fluid at the solid-fluid interface by conduction then the fluid stream absorbs and transfers energy as convection.

Classification Of Convective Heat Transfer Coefficient:

Convective heat transfer is classified as:

• Forced convection

In forced convection, the fluid is forced to flow by external means, such as fans, stirrers, etc. generally, the magnitude or rate of heat transfer in force convection is greater then that of natural convection. In this mode of heat transfer, the heat transfer coefficient, h, mainly depends on the fluid velocity.

• Free convection

Free convection is also called as natural convection, i.e. fluid flows naturally because of the gravitational and buoyancy forces.

Newton’s Cooling Law For Heat Convection:

Newton’s law of cooling is considered as the basic law for convection; which is stated as:

“The heat transfer per unit area by convection is directly proportional to the temperature difference between solid and fluid which, using proportionality constant called the heat transfer coefficient, i.e.

\[Q=hA(T_{fluid}-T_{solid})\]

Where,

h = Convective heat transfer coefficient; W/m².^oC

 

Dimensionless Numbers Used For Convection Heat Transfer Analysis:

• Reynolds Number

Reynolds number is related to the flow of fluids; specially the transition of flow from laminar flow to turbulent flow conditions. This dimensionless number is used to describe whether the flow is laminar or turbulent; hence this is the main step for the convection heat transfer analysis.

\[Re=\ \frac{\rho DV}{\mu }\]

Where,

ρ = density of fluid

V = average fluid velocity

D = tube diameter [internal]

µ = dynamic viscosity of fluid

• Nusselt Number:

This is actually the empirical correlation of the tube size along with the flow conditions.

\[Nu=\ \frac{hL}{k_f}\]

Where,

h = connective heat transfer coefficient.

L = characteristic length of the tube

k_f = thermal conductivity of fluid

• Prandtl Number

It is the ratio of the kinematic viscosity (υ) to the thermal diffusivity (α). It represents the thermo-physical property of fluid, and is independent of flow conditions.

\[Pr=\frac{\upsilon }{\alpha }=\frac{{cp}_{\upsilon }}{k_f}\]

---------------------------------------------------------------------------------------------------------

Reference books:

• Kirk Othmar, “ Encyclopedia Of Chemical Technology”, vol. 12, 4^th ed. , “Heat Exchange Technology”.


• J.P. Holman, “Heat Transfer”, 10^th edition.


• Eduardo Cao, “Heat transfer In Process Engineering”, chap. 4

----------------------------------------------------------------------------------------------------------

Read More

What Is Convection?

Convection is the mechanism of heat transfer occurs as a result of movement of fluid on a macroscopic scale. I.e. heat transfer due to the mixing of elements in fluid or the heat transferred from a solid surface to the moving fluid.

There are several factors, on which heat transfer by convection depends on, such as fluid thermal conductivity, fluid density, fluid velocity, solid surface roughness, temperature difference between fluid and solid surface, moving fluid turbulence, etc. however, as a general rule, it has been experimentally proven that the higher the fluid velocity, the higher is the convective heat transfer coefficient (some times called as film conductance, because of its relation to the conduction process).

Difference Between Conduction And Convection:

It generally doesn’t make sense trying to differentiate between the conduction and convection; as it is the same energy, which is transferred by the combined action of conductivity and the movement of the fluid. Initially, the energy is delivered from solid to the fluid at the solid-fluid interface by conduction then the fluid stream absorbs and transfers energy as convection.

Classification Of Convective Heat Transfer:

Convective heat transfer is classified as:

• Forced convection

In forced convection, the fluid is forced to flow by external means, such as fans, stirrers, etc. generally, the magnitude or rate of heat transfer in force convection is greater then that of natural convection. In this mode of heat transfer, the heat transfer coefficient, h, mainly depends on the fluid velocity.

• Free convection

Free convection is also called as natural convection, i.e. fluid flows naturally because of the gravitational and buoyancy forces.

Newton’s Cooling Law For Heat Convection:

Newton’s law of cooling is considered as the basic law for convection; which is stated as:

“The heat transfer per unit area by convection is directly proportional to the temperature difference between solid and fluid which, using proportionality constant called the heat transfer coefficient, i.e.

           

Q = hA (T_fluid – T_solid )

 Where,

            h = Convective heat transfer coefficient; W/m².^oC

Dimensionless Numbers Used For Convection Heat Transfer Analysis:

• ·       Reynolds Number

Reynolds number is related to the flow of fluids; specially the transition of flow from laminar flow to turbulent flow conditions. This dimensionless number is used to describe whether the flow is laminar or turbulent; hence this is the main step for the convection heat transfer analysis.

                                                            Re = ρVD

                                                                      µ

Where,

            ρ = density of fluid

            V = average fluid velocity

            D = tube diameter (internal)

             µ = dynamic viscosity of fluid

•  Nusselt Number:

This is actually the empirical correlation of the tube size along with the flow conditions.

                                                            Nu = hL

                                                                     k

Where,

            h = connective heat transfer coefficient.

            L = characteristic length of the tube

            k = thermal conductivity of fluid

• Prandtl Number

It is the ratio of the kinematic viscosity (υ) to the thermal diffusivity (α). It represents the thermophysical property of fluid, and is independent of flow conditions.

                                                            Pr = υ = c_p υ

                                                                   α      k_f

--------------------------------------------------------------------------------------------------------------

Reference books:

• Kirk Othmar, “ Encyclopedia Of Chemical Technology”, vol. 12, 4^th ed. , “Heat Exchange Technology.

• J.P. Holman, “Heat Transfer”, 10^th edition.

• Eduardo Cao, “Heat transfer In Process Engineering”, chap. 4

--------------------------------------------------------------------------------------------------------------

Read More

What is conduction?

The heat transferscience and its basic concepts have already been discussed in details. This post is about the Conduction phenomena in detail.

What Is Conduction?

Conduction is the phenomena of transfer of energy due to the temperature gradient. On the molecular level, conduction definition can be described as the transfer of kinetic energy between the molecules;due to the elastic and inelastic collisions between the molecules.

The term conduction is basically used for the heat transfer between the solids. In liquids and gases pure conduction can not exist.

Fourier’s Law Of Heat Conduction:

 Fourier law is used as the general equation of conduction. Fourier law states that:

“The rate of heat transfer per unit area is directly proportional to the normal temperature gradient.”

\[Q=\ -kA\ \frac{dT}{dx}\]

or

\[q_x=-k\frac{dT}{dx}\]

The negative sign of the equation shows the negative temperature gradient, which ensures that the thermal energy flows in the direction of decreasing temperature.

Where:

Q= rate of heat transfer

A= heat transfer area

k  = thermal conductivity of material; W/m.K

q = heat flux ; W/m²

The above two equations are the equations for heat conduction in single direction. As per to the Cartesian coordinates system,the above equations can be simplified as the most general equation of conduction is:

\[q=-k\nabla T\]

Thermal Conductivity Units (k):

Thermal conductivity units in SI system    :   W/m.^oC

Thermal conductivity units in FPS system :   Btu/hr·ft⋅F

Where:

1W/(m. ^oC) = 0.5778 Btu/hr·ft⋅F

One Dimensional Steady State Conduction:

The term steady state conduction describes that the temperatures at any point are independent of the time factor. The one dimensional conduction refers to the fact that the temperature gradients exist along in the single direction only.

• Plane wall:

The heat transfer rate through a plane wall (made up of single material) is :

\[Q_x=-\frac{kA}{\triangle x}(T_2-T_1)\]

            Or

\[Q_x=\frac{T_1-T_2}{R_th}\]

            Where R_th is the resistance to the heat transfer, which is equal to the Δx/ kA

• Composite wall:

The heat transfer rate through a composite wall made up of more then 1 material is :

\[Q_x=\frac{{\triangle T}_{overall}}{\Sigma R_{th}}\]

• Cylinders:

The heat transfer rate along the cylinder are:

\[Q=\frac{2\pi Lk(T_i-T_o)}{{\rm ln}⁡(\frac{r_0}{r_i})}\]

• Spheres

Spherical systems are also considered as the one dimensional systems. The heat transfer rate along the sphere is:

\[Q=\frac{4\pi k(T_i-T_o)}{\frac{1}{r_i}-\frac{1}{r_0}}\]

Read More

What is conduction?

The heat transfer science and its basic concepts have already been discussed in details. This post is about the Conduction phenomena in detail.

What Is Conduction?

Conduction is the phenomena of transfer of energy due to the temperature gradient. On the molecular level, conduction definition can be described as the transfer of kinetic energy between the molecules; due to the elastic and inelastic collisions between the molecules.

The term conduction is basically used for the heat transfer between the solids. In liquids and gases pure conduction can not exist.

Fourier’s Law Of Heat Conduction:

 Fourier law is used as the general equation of conduction. Fourier law states that:

“The rate of heat transfer per unit area is directly proportional to the normal temperature gradient.”

Q = -kA dT

           dx

Or

q_x = -k dT

            dx

The negative sign of the equation shows the negative temperature gradient, which ensures that the thermal energy flows in the direction of decreasing temperature.

Where:

            Q = rate of heat transfer

            A = heat transfer area

            k  = thermal conductivity of material; W/m.K

            q  = heat flux ; W/m²

The above two equations are the equations for heat conduction in single direction. As per to the Cartesian coordinates system, the above equations can be simplified as the most general equation of conduction is:

q = - k ▽T

Thermal Conductivity Units (k):

Thermal conductivity units in SI system    :   W/m. ^oC

Thermal conductivity units in FPS system :   Btu/hr·ft⋅F

Where:

1 W/(m. ^oC) = 0.5778 Btu/hr·ft⋅F

One Dimensional Steady State Conduction:

The term steady state conduction describes that the temperatures at any point are independent of the time factor. The one dimensional conduction refers to the fact that the temperature gradients exist along in the single direction only.

• Plane wall:

The heat transfer rate through a plane wall (made up of single material) is :

Q_x = - kA ( T₂ – T₁)

               Δx

            Or

Q_x =  T₁ – T₂

           R_th

            Where R_th is the resistance to the heat transfer, which is equal to the Δx/ kA

• Composite wall:

The heat transfer rate through a composite wall made up of more then 1 material is :

Q_x  =  ΔT_overall

             ∑R_th           

• Cylinders:

The heat transfer rate along the cylinder are:

Q=  2πLk (T_i – T_o)

ln(r_o/ r_i)

• Spheres

Spherical systems are also considered as the one dimensional systems. The heat transfer rate along the sphere is:

                                                         Q = 4πk (T_i – T_o)

                                                           1/r_i  - 1/r_o

Read More

What Is Viscosity?

Viscosity is the fundamental characteristic property of all fluids. It is usually defined as the measure of internal friction or resistance of the fluid. It can also be termed as the drag force and can be defined as the measure of the frictional properties of the fluid. The study of the behavior of flowing fluid is known as rheology,which has already been discussed in detail.

.

Viscosity is the real factor behind the thickness or concentration of the fluid, i.e. fluid having more viscosity is thicker then the less viscosity fluid hence resists more in the flow. The oil and water are the most common examples of this viscosity and thickness relationship. Oil viscosity is greater then the water viscosity, that’s why oil is thicker then water, and sustain more resistance in flow then water. Viscosity itself is a complete science, having applications in numerous sectors like petroleum, coating, printing, food and beverages, combustion,image processing, power, environment etc.   

.

Viscosity can be expressed as two distinct forms:

.

• Dynamic viscosity

Dynamic viscosity is also named as Absolute viscosity. It is basically the tangential force per unit area, which is required to drag one layer of fluid to another.

.

Mathematically, the above described phenomena can be written as:

.

τ  = F / A

.

            This equation can also be written in the differential form:

       

   τ  = µ (∂u / ∂y)

            Where:

                                   τ          =          shearing stress

µ          =          dynamic viscosity

∂u/∂y   =          velocity gradient

           

• Kinematic Viscosity

Kinematic viscosity is simply the dynamic viscosity of the fluid divided by the density of the fluid. Mathematically, kinematic viscosity is expressed as:

υ = µ / ρ

            Where:

                                  υ          =           kinematic viscosity

µ         =           dynamic viscosity

ρ         =          density of the fluid

.

Viscosity Units:

.

The viscosity units are different for different forms of viscosity. i.e.

.

• The dynamic viscosity units are often expressed in CGS units. However common units of dynamic viscosity are:

• CGS units      : Poise , g/cm.s , dyne.s/cm²


• British units : lb/ft.s , lbf.s/ft²

• The kinematic viscosity units are expressed as Stokes (St) , Centistokes (cSt), or m2/s.

.

Viscosity Of Some Common Substances:

.

The viscosity of some most common substances at room temperatures are given below for references.

.

• Viscosity of air                =  10^-5     Pa.S


• Viscosity of water          =  10^-3    Pa.S


• Viscosity of olive oil       =  10^-1     Pa.S


• Viscosity liquid honey    =   10¹    Pa.S


• Viscosity glass                 =  10⁴⁰   Pa.S

Read More